Re-utilisable blasting apparatus assembly applicable for blasting in coal mines



March 5, 1957 sMlTH RE-UTILISABLE BLASTING APPARATUS ASSEMBLY APPLICABLE FOR BLASTING IN COAL MINES Filed May 4, 1953 INVENTOR ffennefl flslzroo/i e Sm if;

ATTORNEYS RE-UTIIJSABLE BLASTING APPARATUS ASSEM- ELY APPLICABLE FOR BLASTING IN COAL MINES Kenneth A. Smith, West Kilbride, Scotland, assignor to Imperial Chemical industries Limited, a corporation of Great Britain Application May 4, 1953, Serial No. 352,641

Claims priority, application Great Britain June 23, 1952 1 Claim. (Cl. 102-25) The present invention relates to an improvement in a blasting assembly of the kind comprising apparatus of the kind comprising a pressure resisting charge container portion of tubular metal construction threaded at least at the discharge end, an internally threaded discharge head threaded at one end to engage with the threaded discharge end of said container and an expendable bursting disc adapted to yield at a predetermined pressure seated between the discharge head and the discharge end of said container so as to form a gas-tight seal, a gasgenerating charge of solid material capable when locally heated to the temperature of decomposition of a selfsupporting exothermic gas-generating decomposition in non-detonating manner under rising pressure conditions, and an electrically actuable local heating element for initiating, when itself actuated, the decomposition of said charge.

In a blasting assembly of this nature the blasting effect is produced by the discharge of the gases into the borehole through ports or the like in the discharge head when the pressure within the container has built up sufficiently to cause the bursting disc to yield and a passage has been opened up between the container and the discharge head. The time taken for the discharge of the gases from the container into the discharge head and through the ports into the borehole after the yielding of the bursting disc is suflicient to result in a comparatively gentle heaving blasting effect, such as is desirable for such purposes as the production of lump coal.

The present invention also relates to blasting apparatus of readily assembled construction and of the kind comprising a pressure resisting charge container portion of tubular metal construction threaded at least at the discharge end, an internally threaded discharge head threaded at one end to engage with the threaded discharge end of said container and an expendable bursting disc adapted to yield at a predetermined pressure seated between the discharge head and the discharge end of said container so as to form a gas-tight seal.

The present invention also relates to an assembly comprising an electrically actuable heating element and a bursting disc as aforesaid.

Considerable success has attended the employment in a blasting apparatus and a blasting assembly of the aforesaid kind of a charge consisting essentially of a mixture of equi-molecular proportions of sodium nitrite and ammonium chloride containing a small proportion of a stabiliser adapted to prevent excessive decomposition occurring during storage of the material at ordinary temperature. An equi-molecular mixture of sodium nitrite and ammonium chloride when locally heated decomposes without flame in self-sustained fashion with the formation of sodium chloride, nitrogen and steam, and under the rising pressure conditions, experienced in the aforesaid blasting apparatus this decomposition once initiated by the local heating element is greatly accelerated and almost immediately the gases are discharged without'flame,

nited States Patent 'ice with the result that blasting operations with a charge of this nature in a blasting apparatus assembly of aforesaid kind isespecially well suited for coal-mining in fiery or dusty mines. It was originally proposed to employ the heating efiect of an electric detonator but in practice a small electric blackpowder fuse has hitherto been employed as the heating element. Although a blackpowder fuse produces flame, the time taken for the decomposition of the stabilised mixture of sodium nitrite and ammonium chloride to build up a pressure suflicient to cause the bursting disc to yield is long enough for the fragments of the electric powder fuse to have burned out before the bursting disc yields.

In a blasting apparatus assembly of the kind described both of the electrical connections to the local heating element have hitherto been provided on the threaded closure member of the container at the end remote from the discharge head, so that in assembling the device with its charge each time it was to be used, it was necessary to screw up the threaded joints at both ends of the tubular container, the heating element having previously been attached to the electrical connections provided on said closure member and the charge having been introduced, usually from the discharge head end of the container before the bursting disc has been placed in position and the joint with the discharge head has been screwed up. This circumstance was not conducive to rapidity of reloading,

and the reloading operation was in practice carried out at a considerable distance from the scene of the blast, and indeed above ground. Moreover, if by accident a sup posedly charged blasting apparatus assembly were delivered to the shotfirer with the electric powder fuse in position but without the charge of the gas producing composition and without the bursting disc there would be a hazard of an ignition of fire-damp when the electric circuit was completed, since the contents of the electric fuse would tend to discharge in a flaming condition through the ports of the discharge head.

The object of the present invention is to provide a blasting apparatus and a blasting assembly of the kind described adapted to be more expeditiously reloaded with a charge of a solid composition capable on local heating of supporting its own decomposition without flame, and which are free from the hazard aforementioned.

According to the present invention a blasting assembly of readily assembled construct-ion comprising apparatus of the kindcomprising a pressure resisting charge container portion of tubular metal construction threaded at least at the discharge end, an internally threaded discharge head threaded at one end to engage with the threaded discharge end of said container and an expendable bursting disc adapted to yield at a predetermined pressure seated between the discharge head and the discharge end of said container so as to form a gas-tight seal, a gas-generating charge of solid material capable when locally heated to the temperature of decomposition of a self-supporting exothermic gas-generating decomposition in non-detonating manner under pressure rising conditions, and an electrically actuable local heating element for initiating, when itself actuated, the decomposition of said charge, is characterised in that at least one of the two electrical lead Wires of said electrically actuable local heating element is insulated and passes through the bursting disc forming with it an insulated gas tight seal and a free end at least of a length to permit it to be passed through the wall of the discharge head.

' When the non-discharge end of the apparatus in the assembly of the invention is threaded a threaded closure member is provided to engage with said non-discharge end.

In a preferred embodiment of the invention the bore of the container portion at the bursting disc end is suflicient to enable the charge of the gas-producing composition to be introduced in pre-packed form, which has not hitherto been possible since hitherto the bore at both ends of. the container portion has beenv greatly reduced. The bursting disc, which is preferably of. steel, is. provided with a hole, preferably through its, centre, and has attached firmly on one side of it a metal sleeve whose bore is in line with said hole so as to permit at least one insulated electrical lead wire to pass through said hole and boring and to be fixed in said sleeve by a plug of sealing material. If desired one of the insulated electrical conductors may be connected to the sleeve itself, as it will be understood that the sleeve is in electrical connection through the disc with the metal body of the blasting apparatus.

The present invention also includes a blasting apparatus of readily assembled construction and of the kind comprising a pressure resisting charge container portion of tubular metal construction threaded at least at the discharge end, an internally threaded discharge head threaded at one end to engage with the threaded discharge end of said container and an expendable bursting disc adapted to yield at a predetermined pressure seated between the discharge head and the discharge end of said container so as to form a gas-tight seal characterised in that said bursting disc has at least one insulated electrical lead Wire of an electrically actuable local heating element passing through it and forming with it an insulated gas tight seal and a free end at least of a length to permit it to be passed through the wall of the discharge head.

When the non-discharge end of said apparatus is threaded a thread closure member is provided to engage with said non-discharge end.

Preferably the bore of the container portion at the bursting disc end is sufficient to enable a charge of gas producing composition to be introduced in pro-packed form.

It is also desirable that the bursting disc should prefen ably be of steel, should be provided with a hole preferably through its centre, and should have attached firmly on one side a metal sleeve whose bore is in line with said hole so as to permit at least one insulated electrical lead wire to pass through said hole and bore and to be fixed in said sleeve by a plug of sealing material.

The present invention also includes an assembly comprising an electrically actuable heating element wherein at least one of its two electrical lead wires is insulated and passes through a bursting disc forming with it an insulated gas-tight seal and a free end.

It will be understood that it is impossible for the operator to insert the local heating element to be loaded into the tube Without at the same time applying the disc to its proper position, and practically impossible for the operator to fail to notice the presence or absence of the charge of the gas-producing composition when he is inserting the local heating element. For a pre-packaged charge tr e package is desirably recessed so as to accommodate the heating element. It is preferable that the local heating element shouldbe itself incapable of producing an ignition of fire-damp when the electric circuit is completed, so that even an imperfect gas seal with the bursting disc will not result in an ignition. When a local heating element of this kind is used any accidental actuation of it even outside of the apparatus, for instance by stray currents, will not result in the ignition of a fiery or dusty atmosphere and reloading may safely take place below ground close to the mine face.

The invention is illustrated with reference to the diagrammatic drawings accompanying the specification of which Fig. 1 represents a longitudinal section of a blast-' ing apparatus in accordance with the invention shown with the gas producing charge and heating element in position and assembled ready for the blast. Fig. 2 is a detail of a portion of the expendablepart of. the. apparatus somewhat'difierent inform fromnthatiillustratedin Fig. 1.

Referring to Fig. 1 the tubular container portion of the apparatus 1 is of high tensile steel and its external surface is threaded for some distance at each end, the actual end surfaces being accurately faced. The bore of this portion is cylindrical for the greater part of its length but is somewhat diminished at one end. The steel closure cup 2 is internally threaded for some distance from its open end as shown at 3, and has a reduced thickness of metal extending beyond the closed cup recess pierced by an eye 4. through the reduced thickness of the metal. This eye serves to facilitate the withdrawal of the assembly from the debris after firing, and also providesmeans whereby an earth wire 5 may be expeditiously connected to the blasting assembly from without. 6 is a soft copper gasket seated in the recess of the closure cup 2' so that when the faced narrower end surface of the container portion 1. isxbrought to bear upon it by screwing up the threads 3 a gas-tight sealed joint is formed. 7 is a cylindrical packet containing a charge of a pulverulent composition consisting of 53% to 57% sodium nitrite, 41% to- 44% ammonium chloride and 1% to 3% magnesium oxide, into one end of which there is a recess, the recessed end of the packet facing the discharge end of the assembly. Thepurpose of this recess is to accommodate the ventless electrically actuated local heater 3, which has a copper easing into which there is compressed a heating charge 11 consisting of a mixture of antimony and potassium permanganate. The mouth of the casing of the heater is crimped around a plug of a polymerised chloroprenc composition through which pass insulated conductors 9 and 9 leading to an electric matchhead 10, positioned so that the deflagration of the matchhead composition will initiate the strongly exothermic reaction between the antimony and the potassium permanganate in said mixture. The heat conducted through the copper casing initiates the decomposition of the sodium nitrite-ammonium chloride-magnesium oxide mixture in the recessed portion of the local heater 8, and the decomposition is thereafter rapidly transmitted through the whole of the charge in the packet 7. 12 is a steel venting head in the form of an elongated cup having an internally threaded shouldered counter-bore, the shoulder being cut accurately to form a seating for a steel disc 14 adapted to burst at a predetermined pressure sufficient to produce a blasting effect. This bursting disc14' has a small central perforation drilled through it, and on one side of the disc there is welded co-axially positioned a copper sleeve 15 into the open end of which there is forced a tube made of a polymerised chloroprene composition 16 through which there pass the insulated conductors 9 and 9' from the ventless' electric local heating element 8. One of the conductors 9 facing the plug 16 is bared at its end and soldered or brazed to the sleeve 15, the other conductor passing through the central hole in the disc 14 and outwardly through a small boring 18 in the end wall of the dis-charge head to the live terminal of a firing switch connected to a battery some distance from the scene of the blast. The firing switch and battery are not shown in the drawing. 17 is an annular soft rubber gasket bonded to that surface of the disc 14' hearing the sleeve 15, this gasket 17 assisting the operator to make as gas-tight a joint as possible when the threads of the discharge head 12 are screwed up over those on the exterior surface of the container portion 1. The discharge ports 13 from the interior to the exterior of the discharge head 12 are inclined at such an angle that the reaction to the escape of gas from the interior of the discharge head is away from the threaded end thereof towards the end closed but for the boring 18. It will be understood it is the discharge head end of the assembly that is inserted first into the borehole. The weight of the charge in the packet 7 is sufficient to generate a ga pressure exceeding the pressure at which thedisc 14 will burst.

In assembling the device: the closure member is pref-- erably firstoscrewed. home against the gasket 6 so-that the closure at the narrower end of the container portion 1 is already gas-tight before it comes to the hands of the shotlayer, who also receives in a completed state an assembly of the bursting disc 14 carrying the sleeve 15 and gasket 16 with the conductors 9 and 9' and the electric local heater 8 attached to it, the greater part of the length of the insulated conductor 9 beyond the plain surface of the disc being coiled up for convenience. The shotfirer first makes a recess in one end of the package containing the charge 7 and inserts local heater 8 into the recess. He then slides the package into the container portion 1 with the heater facing him and rests the gasket side of the disc 14 on the annular end face of the container portion 1. The leading wire coil is unwound and the free end is threaded through the hole 18 at the end of the discharge head to emerge to the exterior. The shotlayer then begins to screw the discharge head on to the thread on the external surface of the container portion and continues until a gas-tight joint with the disc 14 sealing 011 the container portion 1 from the discharge head is completed. Part of the length of the insulated conductor outside of the boring 18 is bent over so that it can be led alongside the assembly from the inner end to the mouth of the borehole and so to the firing switch. A few turns of bare wire are thrown around the eye 4 of. the closure member 2, and this bare wire is led to earth.

In Fig. 2 the numerals 9, 9, 14, 15 and 17 have the same significance as in Fig. 1, but the polymerised chloroprene composition plug 16 is replaced by a plug of fusible metal 1? poured through the open end of the sleeve.

What I claim is:

A blasting assembly for use in a reutilisable blasting device comprising a pressure resisting charge container of tubular construction sealed at one end, and a discharge head removably engaged on the other end of said container, said blasting assembly comprising an expendable bursting disc having its peripheral portion sealingly engaged between said discharge head and the discharge end of said container, said disc having an opening therein, a sleeve secured to said disc in surrounding relation to said disc opening, a gas generating charge capable of self-sustained fiameless exothermic decomposition when locally heated, and an electrically actuable heating element, said heating element being arranged in said container with said gas generating charge in a prepackaged form and having electrical lead wires for actuation thereof, at least one of said electrical wires being insulated and passing through the disc opening and said sleeve, and a plug being arranged in said sleeve and cooperating therewith to effect a gas tight seal around the electrical Wire passing through said sleeve.

References Cited in the file of this patent UNITED STATES PATENTS 

